The present invention relates to an image recording apparatus, which performs image recording, such as an electrophotographic apparatus.
There are various types of color image recording apparatuses based on image information from computers or the like.
Among various types of systems, in particular, color image recording by an electrophotographic system forms a color image by forming yellow, magenta, cyan, and black toner images on a recording medium which is a photosensitive member, to superpose these formed toner images on a sheet of paper or on an intermediate transfer member.
This electrophotographic system is high speed and can record a color image with high image quality in comparison with an ink jet printing system or the like.
Therefore, it is expected that, in future information age, recording apparatuses in the electrophotographic system which can output images with high image quality in high speed will be increasingly required
Because this color image recording equipment in the electrophotographic system must fix toner images in high speed, a large amount of heat is applied to a fixing device. As a result, warmed air stays in an upper portion of the fixing device and therefore, environmental temperature in a body of the apparatus gradually rises.
Therefore, if papers pass through an environment in such a state that toner is not completely hardened just after being taken out from the fixing device, the papers are ejected outside the apparatus with the toner being semisolid, and are stacked.
Since it is difficult for the stacked papers to radiate heat, there arises such a problem that the toner in a melted state adheres to the stacked paper. In addition, in maintenance, there is a possibility of an unexpected accident such as operator's heat burn due to the operation of removing a jam in a fixing section that is in high temperature.
Furthermore, if air heated at the fixing section due to operation in long time spreads in the apparatus and temperature in the apparatus rises nearly to a softening point of toner, there is such a possibility that toner in a developing device and waste toner which has not contribute to the image and has to be eliminated are melted.
If the waste toner melts, there is such a possibility that a problem such as filming, which toner deposits on a developing roller, and lock of a drive section such as a motor due to increase of toner transfer load arises.
Because these problems in high speed remarkably appear as apparatuses are miniaturized, in order to realize miniaturization and high speed, it is essential to lower the temperature in the apparatus by exhausting the heat staying in the apparatus.
For this purpose, it is common to provide in the body of the apparatus an exhaust fan, exhausting air, heated by the fixing device, outside the apparatus. However, if the exhaust fan is provided in a central portion of a back face of the fixing device in order to exhaust the heat staying in an upper portion of the fixing device, the airflow is only in both longitudinal ends of the fixing device since the flow of air is intercepted by a paper in such a state that the paper is sandwiched and fed by the fixing device. Hence, although temperature in the end portions of the fixing device is lowered, the apparatus is driven while high temperature in a central portion is kept.
By the way, as a conventional technology removing heat in a fixing device, JP-A-6-43788 specification (U.S. Pat. No. 5,436,709) describes such configuration that an exhaust fan is provided in one end of a fixing device in an axial direction to form airflow in the axial direction in the upper portion of the fixing roller.
However, in this conventional technology, it is described to make uniform axial temperature distribution on a surface of a fixing roller and hence to prevent the degradation of image quality. Nevertheless, it is not disclosed to exhaust the air that is heated and staying in the upper portion of the fixing device.
An object of the present invention is to provide such a small and high-speed color electrophotographic apparatus that the apparatus can stably exhaust heat, staying in an upper portion of a fixing device, outside the apparatus, can solve such a problem that ejected paper adheres to another ejected paper by semisolid toner, and has such maintainability that it is possible to safely release a jam in a fixing section.